Bus arbitration

Selecting among initiators requesting a shared resource. An arbiter grants permission before an initiator starts its bus transaction. Fixed priority can indefinitely postpone a lower-priority requester under continuing higher-priority demand. Rotating priority can provide starvation freedom when every owner releases the resource after bounded work. Neither policy alone determines bus throughput: waiting, setup and target readiness also matter.^[ref]

The permission to use a particular computer bus resource during a specified phase. A pending grant need not authorize immediate use. Arm's AMBA Specification, revision 2.0 (section 3.11.3, figures 3-15–3-17) makes address-path handover depend on completion, and delays data bus ownership relative to address bus ownership. Consequently, a single whole-bus transaction owner is a useful simple model, but does not describe every overlapping implementation.

Here, competition between pending initiators for the same shared computer bus resource. Correct bus arbitration converts this competition into waiting. Simultaneously driving incompatible values on the same electrical lines is a different, erroneous kind of bus contention; multiple pending requests need not cause it.